Coated magnesium or magnesium alloy article



Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE v COATED MAGNESIUM R MAGNESIUM ALLOY ARTICLE Herbert K. De Long and James B. Reid, Midland, Mich assignora to The Dow Chemical Company, Midland, Micla,

a corporation of Michi- The invention relates to coated articles of magnesium and magnesium alloys. It more particularly concerns an improved protective coating and method of producing the same upon magnesium and its alloys, said coating being capable of being dyed in a wide variety of colors.

Heretofore highly protective as well as abrasion-resistant coatings capable of being dyed in many colors have not been commercially available for magnesium and its alloys. It is a desideratum in the art to provide such coatings.

We have discovered that by subjecting magnesium and its alloys to the action of an aqueous solution of an alkali carbonate above the normal boiling point under pressure a strongly adherent, corrosion-resistant coating is produced. This coating, besides being useful as a protection for the mate], has the unique property of being capable of taking a dye so that highly decorative ef- 20 f-ects are obtainable by subjecting the coated article to a dyeing operation.

In carrying out our invention, the magnesium or magnesium alloy article is preferably first cleaned as by wire brushing, sand blasting, acid pickling or bufiing, according to the degree of luster desired in the ultimate coating. The degree of luster depends upon the smoothness of the metal surface before being subjected to the coating operation. For example, sandblasting the metal prepares it to exhibit a relatively dull coating, while bufling or polishing the metal to a bright smooth surface results in the article exhibiting a smooth lustrous, but more or less white, opaque surface.

After having suitably cleaned the article to be coated, it is then subjected to the action of an aqueous solution of an alkali carbonate in an autoslave at elevated temperature and pressure, the duration of such treatment depending upon the temperature or pressure employed. The aqueous carbonate solution may be made by dissolving in water from about 2 to 20 per cent or more by weight of a soluble alkali carbonate, such as that of lithium, sodium, or potassium. In general, we prefer to employ sodium carbonate in a concentration of about per cent by weight. The temperature to employ may be between about 110 C. and 250 C. or more and the pressure should be'that corresponding to the vapor pressure of the solution at such temperature. Such vapor pressure may be from about to 400 pounds pressure per square inch and may be used advantageously to regulate the temperature of the operation. The duration of the treatment with the alkaline carbonate solution may be from about 1 to 30 minutes or more. At the higher temperatures a relatively short time of treatment, that is, say from 1 to 5 minutes, suffices, 5 min-' utes being preferred at 200 C., which tempera-' o ture corresponds to a vapor pressure of about 225 pounds per square inch. At lower temperatures, say about 110 to 150 C., the treatment should be more prolonged. After such treatment the article should be rinsed and dried. By the foregoingv treatment there is produced upon the article an adherent coating, apparently integral with the article, yet suiflciently flexible to permit moderate bending without fracture. In addition, the coating possesses the property of being capable of being dyed and may be colored practically any desired shade by subjecting the so coated article to the dyeing action at the boil-- ing temperature for about 1-5 minutes of water in which is dissolved from about 0.1 to 0.5 per cent of a soluble dye.

The following dyes are illustrative of those suitable for the dyeing operation, the number opposite the dye name being that of the Color Index, 1st edition, January 1924., published by the Society of Dyers and Colourists, Assurance BuildingsfBradford, Yorkshire, England:

Color Dye index No.

Pontacyl Light Green SF Yellowish 670 Malachite Green 657 Wool Green BS 737 J anus Green 133 Aniline Red 677 Methyl Red 211 Pigment Scarlet 3B 216 Fast Crimson 63L 57 Eosine Yellow 7 g Quinaldine Yellow. 801 Indian Yellow (1..-. 146 Naphthol Yellow 5. 10 N itrazine Yellow... 640 Methyl Violet 680 Crystal Violet 6B 681 Methylene Blue 2130 922 A111 e Blue 689 Alizarin Blue 8 1067 Eosine Bluish 771 Benzo Blue 2B 406 lizarin Blue G 1066 Fast Acid Black 2B 3 Diazine Black H Extra 401 Niagara Sky Blue 613 618 Acid Blue-Black 246 Diamine Black BH 401 Orange II 151 Orange GG 27 Methyl Orange 142 Alirarin 1040 Fluorescein 766 I Rosolic A i 724 Bismark Brown 331 Phnnnlnhthnlain 764 Acid Fuchsine 30 Am Fuchsine 6B 154. Rhodamine B 749 Xylene Cyanol FF 715 Cm-hinml 12w Alizarln Oyanine 1050 Bordeaux B 88 Sairanine 6B 843 Lanaiuchsine 6B 54 Dimethyl-ammo-azo-Benzene (Butter Yellow) 19 tive, but also afl'ords excellent protection against corrosive attack and it is resistant to mechanical abrasion. These qualities are retained after the article is dyed.

Other modes of applying the principle of Our invention may be employed instead of those ex- I plained, change being made as regards the steps 'temperature above its normal boiling point, said coating being capable of being dyed.

2. Anarticle formed of a metal selected from the class consisting of magnesium and magnesium alloys and having an adherent corrosionresistant coating integrally bonded thereto formed by the action of a liquid aqueous solution of sodium carbonate under pressure at a temperature above its normal boiling point, said coating being capable of being dyed.

3. The method of producing a corrosion-resistant coating upon an article formed oia metal selected from the class consisting of magnesium and its alloys which comprises subjecting the article to the action of an aqueous alkali carbonate solution under pressure at a temperature above the normal boiling point or the solution.

4. A method of producing a corrosion-resistant coating'upon an article formed 01' a metal selected from the class consisting of magnesium and its alloys which comprises subjecting the article to the action of an aqueous solution containing from 2 to 20 per cent of sodium carbonate under pressure at a temperature above the normal boiling point of the solution.

5. A method of producing a corrosion-resistant coating upon an article. formed of a metal selected from the class consisting of magnesium and its alloys which comprises subjecting the article to.the action of an aqueous solution con taining a soluble alkali metal carbonate under: pressure at a temperature above .the normai boiling point of the solution and subsequently dyeing the article by immersion in an aqueous solution of a dye.

HERBERT K. D: LONG. 1 JAMES B. RED). 

